Caller ID is a common service offered by most telephone companies which determines and communicates the number/name of the calling party of an incoming call. Many modern telephone and telephony systems routinely offer this service, which is also known as Automatic Number Identification (ANI). Today, many communication systems provide messaging and conferencing services via packet-based networks, i.e., those that operate in accordance with the Internet Protocol (IP).
Extension Mobility (EM) is a feature that allows users to configure, on a temporary basis, any available IP Phone (appropriately equipped) as their own personal phone simply by logging in to that phone. Once a user logs in, the phone assumes the user's default device profile information, including line numbers, speed dials, services links, and other user-specific properties of a phone. For example, when user A occupies a desk and logs in to the phone, her directory number(s), services, speed dials, and other properties appear on that phone; but when user B uses the same desk at a different time and logs to the same phone, the phone assumes the new user's default device profile and his information appears. The EM feature also allows a called party know who is calling irrespective of where the user is calling from (e.g., office lobby, different cubicle, break room, etc.) or what phone device is being used to place that call. This approach is particularly useful in work environments in which employees do not routinely conduct business in the same place every day.